Machines and related methods for forming, filling and sealing of flexible, pillow-shaped bags made from continuous film are widely used to package a variety of loose products, such as snack foods, frozen foods and the like. These machines typically comprise a supply of packaging film in the form of a web, a tube former for converting the web into a continuous, vertically extending hollow tube and a reciprocating carriage with opposed jaws for stripping, sealing and cutting the tube into a series of filled bags. One of the most successful approaches for stripping/sealing calls for mounting of the stripper/sealing jaws on a carriage that is driven for reciprocating/oscillating movement in the direction of bag forming.
The sealing jaws in a typical packaging machine or method of this type are brought together in two steps. The first step closes the sealing jaws just sufficiently to bring the attached plate-like stripper jaws, which are usually mounted just below the sealing jaws, into engagement to flatten the film tube. The stripper jaws are moved downwardly faster than the constant rate of movement of the film/tube. In this way, the stripper jaws are effective to strip any product from the zone of the tube immediately above, which is the area subsequently to be sealed. The second step completes the closing of the bag by slowing the longitudinal movement of the stripper/sealing jaws to synchronize them with the film and then bringing the sealing jaws together to form the seal and to cut the bag just formed from the tube.
After each bag is formed, the feed of the film/tube is stopped and the strippers/jaws move in the reverse direction back to the top dead center (TDC) position in readiness for producing the next bag. In the early machines of this type, the film/tube feeding is typically provided by pulling the film through the movement of the carriage; however, it is also taught in later efforts to assist the feeding by employing powered rollers or belts on opposite sides of the tube along the forming mandrel of the machine. In order to produce longer bags, the machines typically provide a longer carriage stroke and/or longer assisted film movement. While these intermittently operating machines and methods have worked well in the past, the speed has been limited.
The next step that has taken place relatively recently is a machine enhancement wherein continuous film feed is employed to thereby provide increased speed of operation of the packaging system. In this arrangement, the film feed by the carriage in synchronization with the roller or belt film feed takes up only part of the bag forming cycle; that is, during the bag forming movement of the carriage in the downward direction. As the carriage returns to the TDC position, the film continues to move with the carriage being synchronized to follow the feeding of the film, which as far as we are aware is maintained substantially constant. A typical arrangement in this respect is shown by the Gaukler U.S. Pat. No. 4,974,396, issued Dec. 4, 1990. While this arrangement is an improvement over the intermittent system, it still leaves much to be desired in terms of attaining the desired higher packaging speeds of upward to 120 bags per minute.
In this regard, we have discovered that the bottle neck in realizing the higher speeds is the inability to reciprocate or oscillate the stripper/sealing jaw carriage with the greater acceleration/deceleration that is required. For successful stripping, as well as other ancillary operations, such as blousing of the bag, more rapid acceleration/deceleration to obtain the proper movement relative to the continuous and constant film/tube movement is necessary. The techniques used heretofore, such as the mechanical crank and lever arrangement, even with a servo motor used as the power source for operating the carriage, are simply incapable of rapid enough acceleration/deceleration.
Other approaches have been tried to increase the output of form, fill and seal packaging machines, such as converting the reciprocating carriage to a large, rotating head employing in effect multiple carriages. These carriages are supported in a circle, or along an extended endless path, to allow continuous rather than intermittent operation. As is readily apparent, employing an arrangement of this type is very costly in that each extra carriage represents a substantial cost add on for a machine. Furthermore, each additional carriage adds substantial mass, and thus operating inertia to the rotating head assembly, making it very difficult to change the movement of each carriage to make any necessary correction in timing.
Furthermore, with each of the prior art devices, the speed of movement of the carriage or carriages, must be increased to provide larger or longer bags. Thus, each time a package size change is made, a change must be made in any downstream handling system, such as in the case of the use of a case packer or an individual bag in a box loading machine. As a result, the case packer or loading machine must either be reduced in speed, or a second form, fill and seal packaging machine brought on line, along with a separate conveying and synchronizing conveyor system, such as shown in the Schommartz U.S. Pat. No. 5,092,450, issued Mar. 3, 1992. The requirement for multiple machines, as well as the elaborate conveyor/synchronizer adds additional expense to the packaging line.
While these shortcomings have been tolerated in the prior art, there have been some advances that have successfully allowed increases in speeds and packaging efficiency that are sorely needed in the industry. This even includes improving the relative longitudinal movement (Y axis motion) of the carriage and/or film/tube, which was originally contemplated for intermittent motion machines/methods. One of these new systems for improved feeding of packaging film by the use of computer controlled stepper motors is set forth in U.S. Pat. No. 4,727,707, issued Mar. 1, 1988, and assigned to the same assignee as the present invention. The feeding of the film is maximized in terms of speed and efficiency and can be controlled in order to adapt the machine for an infinite variety of bag sizes. In this particular case, the intermittent film feed is maximized in terms of speed and efficiency by constantly accelerating the film over the first half of the driving time, and constantly decelerating the film over the remaining half. By changing the speed of the carriage, and thus the stripper/sealing jaws, the proper stripping and sealing functions can be obtained.
From this advancement in a machine with the single reciprocating/oscillating carriage, the next step in the advancement of the technology turned out to be controlling the in and out movement of the stripper/sealing jaws so as to be just the right amount needed for a particular bag girth. In addition, in a similar manner, advances have been made to minimize the length of the carriage drive with the stripper/sealing jaws so as to be exactly according to bag size. These advancements to maximize packaging speed and efficiency with the primarily prior art intermittent film feed concept are shown in U.S. Pat. Nos. 4,996,825, issued Mar. 5, 1991 and 5,062,253 issued on Nov. 5, 1991, also assigned to the present applicant.
At the time these advances were made, it is felt by many in the industry that the form, fill and seal packaging operation had been brought to the optimum operating speed and efficiency where a reciprocating/oscillating carriage with its attendant cost and efficiency of operation advantages are concerned. However, we have recently discovered that a key additional advance is possible in the area of controlling and coordinating the relative movement of the packaging film/tube and the carriage that mounts the stripper/sealing jaws. More specifically, the improvement is possible in the area of assuring that the factor of the mass, and thus the inertia, of the carriage is removed as a limiting factor in the performance of the stripping and sealing operation. As a result, the speed and efficiency of a packaging machine or method utilizing a single reciprocating/oscillating carriage can rival the speed of operation of the much more costly machines utilizing the rotating head assembly type machines with multiple carriages.